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Retainer

The term '''retainer''' has several distinct meanings across different fields. In professional services, a retainer is an upfront fee paid by a client to secure the ongoing availability and services of a professional, such as a lawyer or consultant, often on a recurring basis.^[1] In historical and social contexts, a retainer refers to a dependent or vassal who provided personal or military service to a lord or noble in exchange for protection, land, or a stipend, particularly in feudal systems of medieval Europe and Japan.^[2] In orthodontics, a retainer is a custom-made device worn to maintain teeth in their corrected positions after orthodontic treatment like braces, preventing relapse.^[3] In mechanical applications, a retainer is a component that secures and spaces other parts, such as the cage in ball bearings that separates and positions the rolling elements.^[4]

Professional Services

Retainer Agreements

A retainer agreement in professional services refers to a contractual arrangement in which a client makes an advance payment to a professional—such as a consultant, freelancer, or accountant—to secure their availability for future work.^[5] This model functions as a work-for-hire contract that positions itself between isolated project-based engagements and ongoing full-time employment.^[6] By committing to regular or upfront fees, clients gain priority access to the professional's expertise, while providers benefit from predictable revenue streams.^[7] The primary purpose of retainer agreements is to guarantee the professional's dedication to the client's needs over time, fostering consistent service delivery without the need for repeated negotiations.^[8] They provide professionals with financial stability by converting variable project income into steady payments, allowing better resource planning and reduced client acquisition efforts.^[9] Additionally, these agreements delineate the scope of services, setting clear expectations to minimize disputes and align on deliverables.^[10] Key components of a retainer agreement typically include the fee structure, which may involve a lump-sum advance or recurring payments such as monthly installments; the agreement's duration, often spanning months or years; a detailed description of covered services to avoid scope creep; provisions for refunds or unused funds; and clauses outlining termination conditions, such as notice periods or breach remedies.^[10]^[11] These elements ensure transparency and protect both parties by addressing potential contingencies like changes in project demands or early endings.^[12] Common applications include monthly retainers for marketing consultants, where clients pay a fixed fee for ongoing advisory services like campaign strategy and performance analysis.^[7] Another example is a one-time retainer fee for freelance designers, enabling them to reserve time and prioritize a specific client's branding projects ahead of ad-hoc opportunities.^[13] Retainer agreements emerged in 20th-century business practices, particularly within the growing field of management consulting, as a way to bridge short-term contracts and permanent roles by enabling long-term client relationships.^[14] For instance, in 1973, Bain & Company proposed a $25,000 monthly retainer to Union Carbide, marking a shift toward sustained engagements rather than brief projects.^[14] This development reflected broader economic changes, including the expansion of specialized services amid industrial growth.^[14]

Legal and Ethical Considerations

In legal practice, retainer agreements serve as advance payments to secure an attorney's services, but they are subject to stringent ethical and regulatory oversight to protect clients from exploitation. The American Bar Association (ABA) Model Rule 1.5 mandates that all fees, including retainers, must be reasonable, with factors such as the time and labor required, the attorney's experience, and the results obtained determining reasonableness.^[15] Client consent is required for the fee structure, which must be communicated in writing before or within a reasonable time after commencing representation, ensuring transparency and preventing disputes over unearned portions.^[16] In May 2024, the ABA issued Formal Ethics Opinion 505, clarifying that no legal fee may be deemed nonrefundable and that advance fees, including retainers, must be deposited into a client trust account until earned by providing legal services.^[17] Legal retainers are categorized into three primary types: security retainers, advance payment retainers, and evergreen retainers. A security retainer involves funds deposited into a client trust account to cover future services, remaining the client's property until earned through work performed.^[18] An advance payment retainer, sometimes called an "earned on receipt" fee, is considered earned immediately upon payment but requires a clear written agreement specifying this arrangement and must still comply with reasonableness standards under ABA Rule 1.5.^[19] Evergreen retainers function similarly to security retainers but include a provision requiring the client to replenish the account when it falls below a predetermined threshold, such as 50% of the initial amount, to maintain ongoing availability of funds.^[20] Ethical guidelines emphasize safeguards for unearned fees, particularly through Interest on Lawyers' Trust Accounts (IOLTA) programs, which require attorneys to deposit advance retainers into interest-bearing accounts until the fees are earned, with interest benefiting legal aid services.^[21] This prevents commingling of client and attorney funds, a violation punishable by disciplinary action. State-specific regulations vary; for instance, California's Rule 1.15 permits "earned on receipt" retainers with client consent but strictly prohibits commingling, mandating separate trust accounts for unearned portions.^[22] In contrast, New York's Rules of Professional Conduct outright ban nonrefundable retainers, treating them as advances that must be refundable if services are not fully provided, with written engagement letters required to detail fee terms.^[23] Risks associated with retainer agreements include overbilling and challenges to nonrefundable clauses, which can lead to ethical complaints or litigation. A notable case is In re Cooperman (1993), where the New York Appellate Division suspended an attorney for two years after finding that his nonrefundable retainers constituted excessive fees and failures to refund unearned portions in multiple client matters, underscoring that fee size alone does not justify nonrefundability if it exceeds reasonable value.^[24] Globally, retainer practices differ between common law and civil law jurisdictions, with the European Union imposing robust consumer protection under Directive 93/13/EEC, which deems unfair terms—such as one-sided nonrefundable clauses in legal service contracts—non-binding on consumers, prioritizing transparency and balance over common law flexibility in fee arrangements.^[25] In civil law systems like those in France or Germany, retainers are often regulated as deposits under general contract codes, subject to mandatory refund provisions absent explicit justification, contrasting with the case-by-case ethical scrutiny in common law countries.^[26]

Feudal and Noble Retainers

In medieval Europe, particularly during the 11th to 15th centuries, a retainer was defined as a personal follower or servant bound to a lord through ties of loyalty, often formalized by indentures, annuities, liveries, or fees, distinguishing them from the broader feudal vassals who held land in exchange for service.^[27] These retainers formed the core of a lord's affinity, a socio-political group that supported the noble's authority and influence beyond traditional land-based obligations.^[27] Unlike free tenants, who owed limited, tenure-based duties such as occasional military aid or rents, retainers provided ongoing personal allegiance, often without land grants, emphasizing contractual or quasi-familial bonds.^[28] The origins of this retainer system were deeply tied to the evolution of feudalism in England under the Plantagenet dynasty (1154–1485), where lords increasingly relied on personal retinues to maintain power amid fragmented authority.^[27] Emerging prominently from the 13th century, retainers supplemented the declining feudal levy system, with examples including King Edward I's use of liveried followers for military campaigns and administrative control during his conquests in Wales and Scotland.^[28] By the 14th century, this practice had shifted toward "bastard feudalism," a late medieval adaptation where loyalty was secured through cash payments, clothing (livery), and legal support (maintenance) rather than hereditary fiefs, allowing nobles like the Duke of Lancaster to assemble large affinities for political leverage.^[27] Retainers fulfilled diverse roles, including military service in wartime levies, estate management through oversight of lands and finances, and court attendance to bolster a lord's presence in royal councils or parliaments.^[27] Household retainers, often knights or esquires, received daily provisions and badges symbolizing allegiance, while non-resident ones were bound by indentures promising fees—such as the £10–£20 annual annuities common in the 14th century—for readiness to serve in battles or disputes.^[28] This system enabled lords to project power, as seen in William, Lord Hastings' 1460s retinue of over 90 indentured followers who provided both armed support and influence in local governance.^[28] Socially, retainers organized into retinues or affinities that formed the backbone of noble influence, fostering networks of mutual obligation that extended to gentry and urban allies, and contributing to the dynamics of bastard feudalism as a more flexible, contract-based alternative to classical feudal ties.^[27] These groups amplified a lord's retinue size for prestige, with livery badges worn publicly to deter rivals and signal strength, though they sometimes led to factional violence by prioritizing personal loyalty over royal justice.^[28] The retainer system waned after the 15th century, particularly following the Wars of the Roses (1455–1487), as centralizing monarchs like Henry VII curtailed private affinities through statutes in 1485 and 1504 that banned unlicensed livery and retaining to prevent aristocratic disorder.^[27] The conflicts decimated noble houses, reducing their capacity to maintain large retinues, while rising Tudor administration favored professional bureaucracy over personal bonds, marking the transition to more absolutist rule.^[29]

Retainers in Ancient Societies

In ancient Egypt, retainer sacrifices exemplified the extreme loyalty demanded from dependents during the Early Dynastic Period (c. 3100–2686 BCE), where servants and officials were ritually killed and buried alongside pharaohs to accompany them into the afterlife. Archaeological evidence from royal tombs at Abydos reveals hundreds of such burials, including approximately 318 retainers interred with King Djer in his tomb and surrounding enclosures.^[30]^[31] Scholarly debate exists on whether these sacrifices involved coercion, ritual violence, or possible voluntary elements, with some analyses indicating trauma in remains while others suggest alternative methods like poisoning.^[32] This practice, which underscored the pharaoh's divine power and the retainers' subservience, largely ceased by the end of the First Dynasty around 2800 BCE, evolving into symbolic representations like shabti statues in later periods.^[30] In early China, retainers known as shì (士) emerged as a class of dependent warriors, scholars, and officials serving nobles during the Warring States Period (475–221 BCE) and into the Han Dynasty (206 BCE–220 CE), playing pivotal roles in warfare, administration, and governance. These retainers, often from the lower aristocracy or educated elites, provided military support in the era's incessant conflicts and advised lords on statecraft, as reflected in texts like the Analects where Confucius, himself from the shì class, emphasized their ethical duties.^[33] Archaeological evidence from the earlier Shang Dynasty (c. 1600–1046 BCE) further illustrates retainer loyalty through sacrificial burials at the Anyang royal cemetery, where over 10,000 human remains, including soldiers interred with weapons, highlight ritual violence to affirm elite authority.^[34] Such practices symbolized power and coerced allegiance, with retainers' tombs containing artifacts denoting their functional roles in the afterlife. Scholarly estimates suggest more than 13,000 humans were sacrificed over the site's occupation. Mesopotamian palace dependents, prevalent from the third millennium BCE in city-states like Ur and Mari, functioned as administrative aides, laborers, and militia under royal control, receiving rations in exchange for service within temple-palace complexes. Cuneiform tablets from the Ur III Period (c. 2112–2004 BCE) document these retainers' diverse statuses, from skilled craftsmen to low-ranking servants, who maintained the economic and military apparatus of the palace economy.^[35] In Mesoamerican Maya courts during the Classic Period (c. 250–900 CE), elite followers—often nobles or warriors—served as retainers to k'uhul ajaw (divine kings), advising on rituals, diplomacy, and warfare while residing in palatial compounds that reinforced hierarchical loyalty.^[36] Excavations at Classic Maya sites reveal architectural evidence of these courts, symbolizing elite status and fidelity to rulers.^[37] Across these societies, retainers embodied cultural ideals of power through ritualistic or dependent service, often involving human sacrifice or perpetual obligation, as seen in tomb assemblages that preserved their roles postmortem. This ancient paradigm of loyalty, blending prestige with coercion, laid groundwork for more formalized hierarchical systems in later civilizations, paralleling developments in European feudalism.^[38]

Orthodontics

Types of Orthodontic Retainers

Orthodontic retainers are broadly classified into two categories: removable and fixed designs, each serving to stabilize tooth positions after active orthodontic treatment by counteracting natural relapse tendencies. Removable retainers allow for easier oral hygiene and adjustments, while fixed retainers provide continuous support without relying on patient compliance. Selection between these types depends on factors such as the patient's age, expected compliance, and specific occlusal characteristics, with younger patients often benefiting from fixed options due to higher initial adherence rates that may decline over time.^[39] Removable retainers include the traditional Hawley retainer, consisting of an acrylic baseplate with stainless steel wire clasps and a labial bow for retention and adjustability. Introduced in 1919 by Charles A. Hawley, this design uses polymethyl methacrylate (PMMA) acrylic for the base and 0.71–0.81 mm (0.028–0.032 in) diameter stainless steel wire, offering durability and the ability to allow minor tooth movements for settling.^[39]^[40] Another common removable type is the vacuum-formed retainer, such as the Essix, made from clear thermoplastic sheets like polyethylene terephthalate glycol (PETG) at 0.040-inch thickness, forming a horseshoe-shaped tray that covers the teeth for a discreet appearance. Developed in 1993 by John J. Sheridan, these retainers prioritize comfort and aesthetics but may be less durable, with a tendency to warp or fracture over time compared to Hawley designs.^[39]^[41] Fixed retainers, also known as bonded or lingual retainers, involve a thin stainless steel wire (typically 0.44–0.55 mm or 0.0175–0.0215 in diameter) bonded to the lingual surfaces of teeth, often the lower incisors from canine to canine, using composite resin for a semi-permanent hold. This placement behind the teeth ensures 24-hour retention, making it ideal for patients with compliance challenges, though it poses hygiene difficulties that can lead to plaque accumulation and gingival inflammation. Unlike removable options, fixed retainers require professional removal and are particularly suited for maintaining alignment in the mandibular anterior region where relapse is common.^[39]^[42] Common materials across retainer types include acrylic resins for bases in Hawley designs, stainless steel for wires in both removable and fixed varieties, and thermoplastics such as polyurethane or polyester for vacuum-formed trays, chosen for biocompatibility and strength. Customization begins with dental impressions or, increasingly, intraoral 3D scanning to create precise digital models, followed by fabrication via thermoforming, wiring, or even direct 3D printing for enhanced fit and reduced material waste.^[39]^[43] Orthodontists select retainer types based on patient-specific factors: younger individuals or those with Class II malocclusions may receive fixed retainers for better long-term stability, while compliant adults with open bites might opt for removable vacuum-formed designs to facilitate cleaning. Poor compliance, assessed via patient history, often favors fixed options to minimize relapse risk. Studies indicate that consistent retainer wear, whether fixed or removable, achieves 70–90% success in preventing significant relapse over two years, with fixed retainers showing superior initial stability in the first six months.^[39] Recent innovations include SMART retainers, which integrate microsensors—such as temperature and pressure detectors—into removable appliances to monitor wear duration and transmit data via Bluetooth to clinicians, developed in the 2010s to address compliance issues. These sensor-equipped devices, often embedded in Hawley or vacuum-formed bases, have demonstrated improved adherence by providing real-time feedback, though they remain emerging and not yet standard due to cost and battery life limitations.^[44]^[45]

Usage and Maintenance

After the removal of orthodontic appliances such as braces, the orthodontist fits the retainer to maintain tooth alignment. The fitting process typically involves taking impressions of the patient's teeth and surrounding structures, either through traditional alginate material placed in a tray to create a physical mold or via digital intraoral scans that generate a 3D model for precise fabrication.^[46]^[47] These methods ensure the retainer conforms accurately to the post-treatment dental arch, with the orthodontist making any necessary adjustments during the appointment to achieve a secure, comfortable fit.^[48] The standard post-treatment protocol begins with full-time wear of the retainer, typically for 3 to 6 months, except during eating, drinking, or oral hygiene routines, to stabilize the teeth in their corrected positions.^[49] Following this initial phase, wear shifts to nighttime only, often indefinitely, to counteract ongoing natural tooth movement.^[50] Lifelong intermittent use is recommended by orthodontists to minimize relapse, as teeth tend to shift throughout life even without prior orthodontic intervention.^[51] Proper maintenance is essential to preserve the retainer's functionality and prevent oral health complications. Daily cleaning involves rinsing the retainer in lukewarm water after removal and gently brushing it with a soft toothbrush and mild dish soap, avoiding abrasive toothpaste or hot water which can warp the material.^[52] Weekly, it should be soaked in a specialized cleaning solution or a diluted hydrogen peroxide mixture for 10 to 20 minutes to remove buildup.^[52] When not worn, the retainer must be stored in a ventilated protective case to avoid damage or loss; replacement is generally required every 1 to 5 years, depending on wear and type, or sooner if it becomes ill-fitting or damaged.^[51] For fixed retainers bonded to the teeth, maintenance focuses on thorough brushing and flossing around the wire to prevent debris accumulation.^[53] Common issues with orthodontic retainers include breakage, particularly in fixed types where bond failure occurs in 20 to 30% of cases over 2 years, loss of removable retainers due to mishandling, and plaque buildup leading to calculus, gingival inflammation, or decay, especially around fixed wires.^[39] Warning signs such as teeth shifting, discomfort, or a loose fit indicate potential relapse or the need for professional adjustment, as untreated issues can result in malocclusion recurrence.^[39] Studies on patient compliance highlight the retainer's critical role in preventing relapse, with non-adherence leading to alignment changes in up to 50% of cases within 10 years post-treatment.^[54] For instance, removable retainers require consistent wear to be effective, yet compliance rates vary widely, underscoring the need for patient education to avoid the 30 to 50% long-term relapse observed without proper use.^[55] Fixed retainers offer better initial stability but still demand vigilant hygiene to mitigate periodontal risks.^[39]

Mechanical Applications

Retainers in Bearings

In ball and roller bearings, a retainer, also known as a cage or separator, is a component that maintains even spacing between the rolling elements (such as balls or rollers) to prevent direct contact, thereby reducing friction and wear during operation.^[56]^[57] Common types of bearing retainers include crown retainers, which are simple one-piece designs typically stamped from sheet metal for general-purpose applications; ribbon retainers, consisting of two-piece stamped metal assemblies suited for higher-speed operations due to their lightweight structure; and machined retainers, which offer precision engineering for demanding environments like aerospace, allowing for tighter tolerances and better performance under extreme conditions.^[58]^[59]^[60] Retainer materials are selected based on factors such as load capacity, operating speed, and environmental conditions; common options include pressed steel for cost-effective strength in standard uses, brass for its corrosion resistance and low noise in moderate to high-temperature settings, and plastics like polyamide for lightweight, low-friction performance in noise-sensitive or high-speed applications.^[61]^[62]^[63] Beyond spacing, retainers serve key functions such as guiding rolling elements to maintain proper alignment within the raceways, facilitating uniform lubricant distribution to minimize heat buildup, and withstanding centrifugal forces at high speeds to ensure stability.^[56]^[64]^[63] Failure modes often involve deformation or fracture due to excessive heat, overload, or inadequate lubrication, which can lead to rolling element skewing and accelerated bearing wear.^[65]^[66] The concept of retainers in bearings traces back to sketches by Leonardo da Vinci in the late 15th century, with the first practical caged bearing—a roller type—invented by John Harrison in 1740 for marine timekeeping. Philip Vaughan received a patent in 1794 for an early ball bearing design using loose balls in grooved races to reduce friction in carriage axles, though without a retainer.^[67]^[68] Modern standards for bearing dimensions, including considerations for retainer integration, are outlined in ISO 15 for radial rolling bearings.^[69]

Other Engineering Uses

In mechanical engineering, retaining rings, also known as circlips or snap rings, serve as versatile fasteners to secure components axially on shafts or within housings, preventing unintended disassembly under dynamic loads. These semi-circular or fully circular metal rings are installed into machined grooves, creating a shoulder that retains bearings, gears, or other elements without requiring threaded fasteners, thus reducing weight and assembly time in compact designs. Common applications include automotive components such as constant velocity (CV) joints, where they lock in place to maintain joint integrity during torque transmission, and steering systems to secure wheel hubs.^[70]^[71]^[72] Beyond retaining rings, retainers play a critical role in valvetrain systems of internal combustion engines, where valve spring retainers—typically made from high-strength materials like titanium or chromoly steel—position and compress the valve spring against the valve stem. This ensures precise valve timing and prevents spring migration under high-RPM conditions, enabling reliable operation in performance engines with lifts exceeding 12 mm and speeds up to 8,000 RPM. In aerospace and heavy machinery, similar retainers secure springs in actuators and shock absorbers, compensating for thermal expansion and vibration while minimizing wear on mating surfaces.^[73]^[74]^[75] Spring retainers also find use in manufacturing tooling, such as die sets and injection molds, where they clamp compression or extension springs to maintain consistent force during stamping or forming operations. Constructed from durable alloys, these retainers enhance assembly precision and longevity, supporting applications in high-volume production environments like automotive body panel fabrication. In pneumatic tools, retainers secure springs in hammers and chisels, ensuring energy transfer efficiency and operator safety under repetitive impacts.^[76]^[77]^[78]

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A Guide to Bearing Retainers (cages) for SMB bearings
Cages in 316 stainless steel can be fitted to full ceramic bearings from 8mm bore upwards. Good for low to medium speeds; Can withstand higher temperatures ...Missing: history | Show results with:history
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Guide to Bearing Cage Materials
Most Popular Bearing Cage Materials. Pressed steel cages are made from thin sheet steel formed into shape. They are cost-effective and widely used in standard ...Missing: types | Show results with:types
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A Comprehensive Overview Of Bearing Retainers-FHD
Jun 4, 2024 · Explore key insights on bearing retainers, their types, materials, and benefits for optimal bearing performance and durability.Missing: history | Show results with:history
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Ball Bearing Cages & Retainers - AST Bearings
Material is type 302 stainless steel. Brass and carbon steel are also available. These types of cages can operate at low to moderately high speeds. Loose crimp ...Missing: history | Show results with:history
[57]
Lubricant Failure = Bearing Failure | Machinery Lubrication
Avoiding Lubricant Failures. Anti-friction bearings must be lubricated to prevent metal-to-metal contact between the rolling elements, raceways and retainers.
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The material of the bearing cage and the reasons for the fracture of ...
Jul 22, 2022 · The material of the cage is required to have good thermal conductivity, small friction factor, good wear resistance, strong impact toughness, low density and ...Missing: standards | Show results with:standards
[59]
Failure Modes For Bearings | Emerson Bearing
Jan 4, 2016 · Bearing Failure Modes · Improper lubrication – Lubrication enhances function and prolongs bearing service life, but only if done correctly.
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The History of Ball Bearings - Hartford Technologies
Feb 10, 2017 · Philip Vaughan received a patent for a ball bearing in 1794, and his design became the basic blueprint for the creation of the modern ball ...
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Bearing data | Schaeffler medias
The main dimensions of metric rolling bearings are defined in the following ISO dimension plans: ISO 15:2017 for radial rolling bearings, excluding single row ...
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Retaining Ring Application Examples | Rotor Clip
Retaining rings are used in automotive, aerospace, defense, energy, and medical sectors, including clutches, valves, CV-joints, oil seals, and steering wheels.
[63]
Retaining Ring Application Examples - Smalley
From the watch dial on your wrist to a wind turbine, no application is too small or too big for a retaining ring to secure. Below are a few common applications ...
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What are Retainer Rings, its types and applications
Jan 1, 2018 · Retaining rings are metal fasteners that fit into a groove on a shaft or in a housing or bore to provide a shoulder that holds an assembly in place.
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Valve Retainer Function: Importance in Your Engine's Valve Train
Sep 3, 2024 · A valve retainer, also known as a valve spring retainer, is a critical component within the valve train of an engine. It serves to keep the valve spring in ...
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Performance Valve Springs and Retainers - Engine Builder Magazine
Valve springs can be made smaller and lighter to handle more total valve lift and higher engine speeds without breaking.
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https://resources.hartfordtechnologies.com/blog/the-history-of-ball-bearings
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https://ntrs.nasa.gov/api/citations/19810009866/downloads/19810009866.pdf
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Spring Retainer-Injection Molded Parts - YUU SPRING
Spring Retainers, the epitome of precision in injection-molded parts, excel in securing valve springs within engines. These meticulously crafted components ...Missing: mechanical | Show results with:mechanical
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5pcs Pneumatic Chisel Spring Retainer Durable Air Hammer ...
5pcs Pneumatic Chisel Spring Retainer Durable Air Hammer Springs for Automotive and Mechanical Applications Versatile Compatibility for Pneumatic Tools.<|control11|><|separator|>